Apparatus for extraction



Dec. 2, 1941. A. A. LEVINE ET AL APPARATUS FOR EXTRACTION Filed May l5, 1958 v3 Sheebs- She l IIAIIL mmzwamu W TORN E Y.

INVENTORS.

LEVI NE Dec. 2, l94l.

A. A. LEVINE ET AL APPARATUS FOR EXTRACTION Filed May l5, 1958 5 sheets-sheet 2 DRAIN INVENTORS. 'ARTHUR A. LEVINE ORLAND R. SWEENEY BY CHARLES E. KIRCHER JR.

ILLIAM L. MQCRACKEN ATTORNEY.

De 2, 1941- A. A. L EvlNE ET AL APPARATUS FOR EXTRACTION Filed May 13, 1938 3 Sheets-Sheet 3 INVENTORS.

Patented'Dec. 2, 1941 UNITED STATES PATENT o FFlcE aPrARA'rUs Foa nx'mAc'noN Arthur A. Levine, Niagara Falls, N. Y., Urland B. Sweeney, Ames, Iowa, Charles E. Kircher, Jr., Niagara Falls, N. Y., and William L. McCracken, Ames, Iowa, assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application May 13, 1938, Serial No. 207,760 l veyors positioned in the two legs and horizontal Claims.

.methods to obtain products of commercial value.

The advantages of solvent extraction in obtaining fats, oils and waxes from materials have long been recognized andI a number of solvents such as carbon bisulphide, benzene and various gasoline fractions have been used for this purpose. Distinct disadvantages attend the use of such solvents, however, and as a result, the methods most extensively employed involve the use of either the hydraulic press or the so-called expellor `type screw press The great disadvantage of these two types of equipment is that the pressed material generally contains in the neighborhood of 5 to 10% of unremoved oil or fat which represents a distinct nancial loss.

The chief disadvantages of solvents such as carbon bisulphide or benzene is that they are inammable and highly explosive when mixed with air and as a result of this, many fatal ac- Furthercldents have resulted from their use. more, .these solvents are distinctly toxic in all concentrations. Past experience with such solvents has shown that there is a real need for a non-inammable, non-explosive solvent which is not highly toxic. The chlorinated hydrocarbons such as trichlorethylene and perchlorethylene meet the above requirements for a practical extraction solvent, but their use has been greatly restricted, due chiefly to the fact that a suitable extraction apparatus in which counter-current extraction by means of these solvents may be effected has not been available to the art.

Many types oi extraction apparatus have been proposed and used. Among these may be mentioned one which has been employed quite generally with low specific gravity solvents such as garoline fractions. It consists essentially of two vertical tubes or legs joined at their lower ends by means of a horizontal tube. The solvent is fed in near the top of one leg and leaves the U-shaped apparatus near the top of the other leg. The material to be extracted enters the top of the leg from which the solvent is removed and leaves the apparatus at the top oi the leg at which the solvent enters. Movement of the solid material through the apparatus is effected by means of suitable designed and operated conconnecting tube. l

If the solvent employed has a specic gravity less than that of the oil to b e extracted, then as extraction takes place, the specic gravity of the resulting lixivium will increase as the oil content thereof increases. Hence, in the U- shaped apparatus mentioned above the specic gravity of the lixivium at the top of the legfrom which it leaves the apparatus will be greater than the specific gravity at the bottom, of that leg. The result is that convection currents are set up in that leg of the extractor, 4since the heavier liquid at the top tends to sink while the lighter liquid at the bottom tends to rise. These convection currents cause the mixing of the lixivium in one zone of the extractor with that in another zone so that eiiective counter-current extraction is not obtained. 0n the other hand, this adverse condition does not exist in that leg of the extractor into which the solvent is fed- Here, the specii'lc gravity of the solvent as it enters the upper part of theV leg is lower than that of the lixivium at any point below the point of entry oi the solvent and the specic gravity of the liquid in this leg will increase progressively from top to bottom.

When a solvent, e. g. trichlorethylene orperchlorethylene, having a specilc gravity greater than that of the oil to be extracted is employed in the U-shaped extractor mentioned above, the specific gravity of the lixivium resulting from the solution of the oil will decrease as its oil content increases. Hence, the specific gravity of the liquid at the bottom of that leg into which solvent lis fed will always be less, due to solution of o'il in the solvent, than the specic gravity of the liquid higher up in the leg. As pointed out previously, this condition gives rise to convection currents so that proper conditions for countercurrent extraction are not realizable. The specific gravity of the lixivium as it ows upwardly in the other leg of the extractor will decrease progressively as its oilA content increases and no convection currents will be set up in that part of the apparatus.

It is apparent from the above that the wellknown U-type extraction apparatus is not properly designed for the employment of a solvent having either a higher or lower speciiic gravity than that of the oil to be extracted, since in either case convection currents are formed in some part of the extractor, which results in the mixing of lixivium in one zone withthat in another, The design of any counter-current 'extraction apparatus should always take into consideration the relative specific gravities of the solvent and the oil to be extracted .so that throughout the entire length of the extractor the less dense liquid will always be kept above the more dense liquid. Practically all designsvof apparatus previously proposed have failed to give proper consideration to this important factor. Furthermore, so far as we are aware, no extraction apparatus has yet been used or proposed wherein a solvent having a specific gravity greater than that of the oil, fat or wax which is to be extracted may be used therein in a truly counter-current manner, i. e. so that the travel of liquid throughout the entire length of the extractor is such that the less dense liquid will always be maintained above the more dense liquid.

Accordingly, a special object of our invention is to provide a method and apparatus for the extraction of oils, fats or waxes from solid materials containing such substances by means of a solvent, e. g. trichlorethylene or perchlorethylene, whose specific gravity is greater than that of the oil or like material which is to be extracted, whereby extraction may be carried out in truly counter-current manner. This particular object may be accomplished in accordance with our invention by the use of an apparatus ,of the type i1- lustrated in Fig. 2 of the drawings. A descriptionofthis apparatus, together with an explanation of its mode of operation will follow subsequently.

The removal of residual solvent from solid materials, e. g. soya bean flakes, seed meals and the like, from which oil has been extracted has always presented certain diiculties. For example, it is common practice to remove such residual sol vent from soya bean flakes or meal by heating and by displacement of the solvent vapors with steam. Various methods have been proposed for eiiecting such treatment by passing steam -through the solid material in a direction countercurrent to the movement thereof. However, due to the tendency of soya bean akes to become pasty when wet and to the dimculty previously encountered in providing adequate exposure of tbe solid particles to the displacing action of steam or other inert carrier for residual solvent vapors, an entirely satisfactory removal of residual solvent has not been realized. Since the practical success of any solvent extraction process is dependent upon the economical recovery of the solvent, the need of a more `practical apparatus for effecting recovery of residual solvent from the solid material has long been recognized in the art.

Accordingly, a further object of our invention is to provide an apparatus for use in coniunction with our novel extractor wherebyv recovery of residual solvent from solid material, especially soya bean akes, may be realized in a more simple and economical manner. This object may `be accomplished by employing the equipment illustrated in Fig. 4. A description of this equipment will be given later in the discussion below. Various ancillary objects of our invention will be4 sectional view, shown partly in elevation, of the preferred modification of the extractor proper and F18. 3 is a cross-sectional view taken along line 3-3 of Fig. 2. Fig. 4 is a longitudinal sectional view, shown partly in elevation, of the equipment for removing residual solvent from the solid material as it is delivered from the extractor shownl in Fig. v2.

Referringto Fig. 2, element l is a hopper whose purpose is to supply solid material, e. g. soya bean flakes, to tube 2 of the extractor. Tube 2 is joined at its lower end to a second or riser tube 3 which is inclined towards tube 2 so as to make a slight angle with respect to the vertical. Solid material is discharged from the upper part of riser tube 3 by way of tube 4. The apparatus is mounted so that point D is lower in elevation than point A. This is accomplished by inclining tube 2 at a slight angle from the horizontal, e. g. about 16, as shown in Fig. 2. Screw conveyor 5 is positioned within tube 2 so as to rotate upon thrust bearing 1, and screw conveyor E is mounted within tube 3 so as to rotate upon bearings 9 and I0. These conveyors may be driven by any suitable means, e. g. by gear drives, not shown in the drawings. Fresh solvent is introduced into the extractor by way of inlet pipe I I and lixivium is removed from the upper part of tube 2 by way of slots I2. The lixivium from slots i2 passes through box I3 and is delivered to the system for separating solvent from the extracted oil by way of outlet pipe I4. Screen l5 in box i3 serves to separate from the liquid any coarse solid particles which may have escaped through slots l2. This screen may be omitted if desired, especially when the product lixivium is to be filtered before being processed further. Preferably, one side of box i3 is removable in order to facilitate periodic cleaning of screen i5 or slots i 2. Asis shown in Fig. 3, the removable side l1 may be secured tol the box proper by means of screws i8. Element i6 in Fig. 2 is a drain which may be provided with any suitable valve or cap arrangement not shown in the drawings. Y Its purpose is to provide a means for draining the apparatus of liquid when this is desired and also to serve as a well for collecting any adventitious materia-l, e. g, small pieces of metal or other heavy material, from which such material may be removed without interrupting operation of the extractor.

l'n operation, material to be extracted is fed continuously into the upper part of leg 2 by means of hopper l and is carried through the extractor by the action of screw conveyors 5 and 6. Solid material is discharged from tube 3 by way of down-spout 4. Fresh solvent, fed in continuously by way of inlet pipe Il, flows through the extractor countercurrent to the direction of movement of the solid material therein, and the product lixivium leaves the extractor proper by way of slots l2. In elevation, solvent inlet pipe li should deliver solvent at a point above point A, the liquid level in leg 2. The meal outlet l should be placed several feetabove the solvent level C in leg 3 in order that ample time may be with a section of reverse thread fiighting 8 which facilitates 'discharge of meal into spout I.

An essential requirement of our extractor is that it be designed'to maintain in that part and into the nights of conveyor 6.

thereof where extraction is to be effected liquid of lower specinc gravity always above liquid of higher specic gravity. In this manner the tendency for lixivium in one zone to mix with that in another is practically eliminated' since convection currents in the liquid are reduced to a y 'at the point D contains only a very small amount of oil andhence has a specific gravity` substantially the same as that of the pure solvent. However, as the liquid flows from the point D to the point A its specific gravity decreases progres'- sively due to progressively larger quantities of oil being contained therein. Therefore. the specific gravity of liquid at any given point between D and A will be less than the specific gravity of liquid at any lower point between D and A so that at all times liquid of lower specific gravity will be above liquid of higher specic gravity. Under these circumstances there will be no tendency for convection currentsto -form and exl traction in truly counter-current manner may be realized. Substantially complete extraction in leg 2 may be realized by making this leg sufciently long, by controlling the ratio of solids to solvent yfeci to the extractor and by adjusting:A the rate of travel of material throughv the extractor. By properly adjusting these factors, apparatus such as that illustrated in Fig. 2 permits the obtainment of product lixivium of practically any oil content. In the commercial extraction of oil from soya beans a lixivium con taining 25% oil has been found to be practical. However, a lixivium having a higher oil content may be obtained by adjusting the above mentioned factors accordingly.

An important point of construction of the vapparatus illustrated in Fig. 2 is the angular relationship between the tubes 2 and 3 as well as the position of tube 2 with respect to the horizontal plane. Using a high specic gravity solvent such as trichlorethylene, the ordinary oil, fat or wax-bearing material that is to be subjected to 'extraction will generally have a density less than that of the solvent. Advantage is taken of the property of such material to float in the solvent in securing uniform and continuous movement of material through the extractor. In Fig. 2, the movement of material from tube 2 into the riser tube 3 is effected by allowing the material to oat from the point D upward Once the material has entered tube 3 positive.- upward movement in this tube is obtained by means of the conveyor. Any material which does not oat will be pushed out into tube 3 where it can be picked up by the conveyor in this tube.

The angle which tube 2 makes with the horizontal should be kept small. In practice a suitable angle has been found to be about to 25, although an angle of about to 207 is preferred. This tube is relatively long in comparison with tube 3, in order that practically complete extraction may be effected in tube 2. The extracted l is properly positioned with respect. to the horizontal plane, tube 3 will be in a vertical position. lor inclined from the vertical plane either towards or away from tube 2 at an angle not more than'about 25 Whether or not the shorter or riser tube 3 should be positioned to incline from the vertical plane eithertpwards or away from tube 2 willdepend .largely upon the particular solid material being handled and especially uponwhether the density of the solvent employed is greater or less than that of the solid material. after it has been rendered substantially free of oil. But regardless of what position tube 3 may assume with respect to the vertical plane,

we .have found that for practical purposes this tube should not be inclined from the vertical plane either towards or away from tube 2 at an angle greater than 4about 25, since otherwise an impractically long riser tube would be necessary.

The movement of solid material through -the 'extractor at the junction of the two legs thereof, point D in Fig. 2, may be materially aiected by the position of riser tube 3 with respect to the vertical plane. In the arrangement shown in Fig. 2, tube 2 makes an angle of about 16 with the horizontal and an angle of about 60 with tube 3 so that the latter tube inclines at an angle of about 14 fromthe vertical towards tube 2. As conveyor 5 in tube 2 is rotated, material is forced to move past point D and into tube 3. If the solid material is lighter than the solvent, it will tend to rise vertically and enter the compartments between the flights of conveyor 6. Because tube 3 is inclined towards tube 2, this natural tendency of the material to rise in the solvent will not be hindered by contact of the solid material with the lower side wall of tube 3, so that the filling of the compartments of conveyor 6 will be facilitated by this arrangement.

0n the other hand, if tube 3 were inclined from the vertical away from tube 2, the natural tendency of the lighter solid material to rise vertically in the solvent would be appreciably hindered by contact of the material during its upward travel -with the upper side walls of tube 3. In this arrangementyfilling of the nights of conveyor 6 would depend entirely upon the action of conveyor 5 in tube 2 to force the solid material into the compartments of conveyor 6, and would not be aided by the buoyancy of the solid .material in the solvent. If tube 3 were given a vertical position, the side walls of this tube would oiier a certain resistance to the natural vertical movement of the lighter solid material', but this resistance would not be as great as it would be if tube 3 were inclined from the vertical away from tube 2.

Ihe situation would be somewhat different if the solid material at point D in the extractor, were heavier than the solvent employed. In this case, the natural tendency would be for the material` to sink upon passing point D, so that the filling of the compartments of conveyor 6 would be facilitated by having riser tube 3 inclined slightly. from the vertical away from tube 2 and would be somewhat hindered by the opposite arrangement. Y

It is not necessary, however, to the successful operation of our apparatus that the short riser tube thereof be given any special position with respect to the vertical, regardless of the relative densities of the solvent and the solid material after the oil has been removed therefrom. Thus. excellent results may be obtained .by positioning the two legs of the extractor at right angles to each other. This arrangement permits extending the lower end of the conveyor in the long inclined tube to the extreme lower end of this tube, leaving only enough space between the end of this conveyor and the conveyor in the shorter riser tube for proper clearance. Upon rotation of the conveyors, solid -material would be forced from'the end compartment of the first conveyor directly into the flights of the conveyor in the riser tube with no dead space being left between the conveyors wherein the solid material would be free to rise or sink. In this arrangement it would be of little importance whether the solid material tends to rise or sink in the solvent at the junction of the two tubes.

As stated above, the relatively long extractor tube, tube 2 in Fig. 2, should be positioned so as to make a small angle with respect to the horizontal plane and the relatively short riser tube, tube 3 in Fig. 2, should not be inclined from the vertical plane at an angle more than about 25. It has been found that excellent results may be obtained in accordance with our invention by positioning the long inclined tube at an angle of about to 25 from the horizontal plane, although we prefer that this angle be about to 20. This position of the tube insures a proper specific gravity gradient in the tube when a solvent is employed which has a speciiic gravity greater than that of the oil being extracted. The eiectiveness of so positioning this tube is evident upon considering how the extractor would operate were the tube placed in a horizontal position. In such an arrangement, employing vertical feeder and exit tubes, no practical provision can be made to keep the high density solvent fed from one of the vertical tubes from flowing along the'bottom of' the horizontal extractor tube. Thus, it is evident that the extractor tube should be positioned so as to make a small angle, for example, 10 to 25, with respect to the horizontal plane.

It may be desirable under some circumstances to effect extraction at temperatures either above or below atmospheric temperature. Thus, with some types of oil or fat-bearing materials, extraction is facilitated by operation at temperatures considerably above room temperature. In such cases, the extractor illustrated in Fig. 2 may be provided with suitable heating means for maintaining the desired temperature. Thus, tubes 2 and 3 may be provided with steam jackets or other suitable means adapted to provide the required heat. -If cooling is desired, cooling liquid at the desired temperature may be circulated through jackets provided around the tubes of the extractor. It is therefore to be understood that the apparatus illustrated by Fig. 2 is not restricted to operation at any speciiic temperature.

angles to the axis of the tube, provide a narrow opening at the inner surface of the tube wall and a Wider opening at the outer surface thereof. Ordinarily the lixiviurn will flow out of the lowest slot. However, if this becomes plugged the liquid level in the tube will rise, causing the lixivium to flow out of the next higher slot, and so on up the series of slots.l Provision may be made to clean automatically these slots. For example, light flexible wires may be spaced radially along the shaft of the conveyor in such a way that the spring wires wipe through each slot each time the shaft is rotated. We have found, however, that the flow of lixivium through the bevelled slots in conjunction with the wiping action of the conveyor flights, sufilces generally to prevent permanent clogging.

There are distinct advantages to feeding the solid material into the extractor tube so as to keep the conveyor flights above the lixivium outlet well filled with material. 'I'his maintains a column of solid material above the liquid which absorbs solvent vapors, thus preventing solvent loss. Also, it has been found that when the conveyor is well filled at the point corresponding to the lixivium outlet, the amount of solid entrainment in th'e lixivium is reduced to a minimum due to the filtering action of the column ofsolids. Furthermore, we have found that somewhat better operation is obtained by feeding the entering solid material into the screw conveyor at a point above the lixivium outlet since then the lixivium cannot interfere with the filling of the conveyor flights. It is not necessary, however, that the hopper be placed at the position indicated in Fig. 2. Good results ,may be obtained by feeding in the solids at other points along tube 2, for example at point B.

It should be noted that by inclining the riser tube 3 of the extractor at a slight angle from the vertical, as shown in Fig. 2, it is possible to discharge the meal by the action Yof gravity directly into equipment for removing residual in order to expose a maximum of surface to the solvent and thereby increase the rate of extraction. Seeds, beans, tubers, and the like may be fiaked and animal material may be hashed. Exceedngly ne particles are undesirable in that their separation from the lixivium may become troublesome. We have found that by providing narrow slots, indicated by the numeral I2 in Fig. 2, on the underside of the long extractor tube at the point where it is desired to remove the lixivium, entrainment of solids in the lixivium is greatly reduced. These slots, cut at right /rconsists of a similar member 22.

solvent from the solids. We have discovered that the equipment illustrated in Fig. 4 of the Idrawings is well adapted for treating meal, e. g. soya bean meal, to remove residual solvent therefrom. This equipment consists essentially of a drier section connected with a steamer section, each section being provided with conveyors particularly adapted for the movement of solid material therethrough.

Referring to Fig. 4, tubular member 20 is connected with element 4 of the extractor shown in Fig. 2 and serves to direct material dropping from the extractor into the drier. The drier consists of along tubular member 2| and the steamer Both the drier and steamer are jacketed by steam jackets 23. Running the length of tube 2|' is a conveyor 2l, adapted to rotate in bearings 30 and 3|. The front end of this conveyor is made up of solid screw flights 25 whereas the center or main section consists of two rods wound around a central shaft so as to form two separate screws or spirals of different pitch, indicated in the drawing as elements 26 and 21. The spiral of greatmeans of connecting tube 44, is similar to the drier except that a somewhat different type of conveyor 32 is shown for moving the meal through the steamer. The front end ofl this conveyor is not provided with solid flights and the conveyor proper consists of a rod spiral type screw conveyor, the single spiral being indicated in Fig. 4 as element 33. The nights of this conveyor are supported from the central shaft by struts 34. This conveyor, at the outlet end of the steamer, is similar to the conveyor in the drier in that it is provided with a section of solid, reverse flighting 35. Conveyor 32 is adapted to rotate in bearings 36 and 31. It is to be noted that the flights of this conveyor are provided with horizontal connecting bars 38. These connecting bars are secured, e. g. by welding, to adjacent ights of the conveyor so as not to protrude beyond the outermost extremities of the nights. Preferably, alternate sets of two or three flights are connected by bars 38 on one side of the conveyor, while the intervening sets of two or three ights are connected on the opposite side, as shown in Fig. 4,

since this arrangement preserves the balance of the conveyor. If desired, all of the flights may be connected by similar bar members on two opposite sides of the conveyor, but such an arrangement is generally not necessary.

The drier and steamer are heated by means of steam introduced by way of inlets 39 into steam jackets V23. superheated steam is injected directly intovthe steamer by wayof inlet'di so as to contact .the solid material and displace the last traces of residual solvent. or other inert gaseous carrier may be introduced into the steamer at a plurality of points along tube 22 if desired. Solvent and steam vapors are removed from the apparatus by way of outlet 42 which may lead to a condenser and separator as indicated in Fig. l. Condensate from the steam jackets is removed by means of tubes 40. After all residual solvent has been removed, the meal is discharged from the apparatus by way of a barrel or rotary valve 43. This valve may be operated by mechanical means, not shown, and serves to discharge solid material while at the same time preventing the exit of steam or solvent vapors at this point.

We have discovered that the open flight types of screw conveyors illustrated-in thedrier and steamer of Fig. 4 function admirably wellto convey meal through the equipment for removing residual solvent. The solid ght type of conveyor is not suitable since solid flights hinder the escape of solvent vapors from the meal and obstruct the passage of steam therethrough. On the other hand, the open iiight conveyors of Fig. 4 facilitate thorough contacting of the material with steam or other inert gas. Also, with conveyor 24 having two spirals of different pitch, the spiral of greater pitch 21 continuously turns the material over as it is moved forward by the spiral of lesser pitch 26. Spiral 21 also has a tendency to prevent sticking of meal to the walls of the casing and causes better contact with the heated surface, whereby better drying results. The function of the horizontal connecting bars 38 in conveyor 32 is the same as that of the spiral of greater pitch 2 in conveyor 24. Hence, either of these two types of open. ight conveyor may be used in either the drier or steamer of Fig. 4. The short sections of solid ighting 29 and 35 at the ends of the conveyors shown in Fig. 4 prevent material from packing at the end of the drier and steamer tubes and assist in causing it superheated steam i to fall by vgravity into connecting tube 44 or the discharge tube which feeds barrel valve 43. The iront end of conveyor 24 in the drier is preferably. provided with a section of solid flights at the point where meal from the extractor enters the drier, since this arrangement eliminates the tendency for the meal to plug the drier at this point. Once the meal has been conveyed somewhat past the point, of en/try, no difliculty of this sort is experienced with the open nights.

We have shown in Fig. 4 separate drier and steamer sections connected by means of tube 44. Instead of this arrangement the two sections may be combined into one long tube. the fore part being used as the drier'and the other as the steamer. Such an arrangement is not preferred since it would require an exceedingly'long screw conveyor which might be troublesome in operation. Also, a plurality of drier and steamer sections. joined together as indicated in the drawing, might be used in place of the single drier and steamer as indicated in Fig. 4. But, Whatever arrangement is used, we have discovered that it is most practical to heat the meal to a temperature of atleast about 100 C. before' contacting it with steam.

Solid material, e. g. soya bean meal and the like, as it is discharged from the extractor illustrated in Fig. 2 has a tendency to become pasty and the removal of residual solvent from material which has reached the pasty stage is dinicult. This tendency to become pasty is increased greatly if the meal is subjected to the action of steam before it has been heated to about C. It is therefore highly desirable that the meal be subjected first to an effective drying treatment and thereafter to the action of superheated steam to remove the final traces of solvent. As a result of numerous experimental trials it wasfound that substantially complete removal of residual solvent may be accomplished with a minimum of difficulty resulting from the meal becoming pasty when the drier and steamer arrangement, including the special opentype conveyors, illustrated in Fig. 4 is used.

Fig. 1 shows schematically an effective assembly of the extractor shown in Fig. 2 and the drier shown in Fig. 4, in conjunction with equipment for separating solvent from the extracted oil and for recovering solvent from the steamer and drier. In general plan', solid material is passed through a crusher, a aker and nally into the extractor, through which it then passes in a manner truly counter-current to the direction of movement of the solvent. The solid material then falls from the top of the riser Apipe of the extractor into the drier, from whence it passes through the steamer and is discharged therefrom by means `of the barrel valve. The

solvent enters the short or riser leg of the extractor and lixivium is removed from the slotted arrangement previously described, from whence it passes through filters for removing :finely divided, suspended, solid material. The lixivium is then preheated and passed through a stripping still where final traces of solvent are removed from the extracted oil. The solvent vapors pass into the condenser where they are condensed and separated from water to provide solvent which may be used again in the process. An absorption tower is also provided to recover solvent vapors carried by the inert or non-condensible gases from the condenser, extracted oil being used as the absorbing medium. Oil and recovered solvent from the absorption tower are fed into the preheater together with lixivium from the extractor. ratus shown in Fig. l is highly eiective and permits extraction of oil and similar materials to be accomplished without undue loss of solvent.

Our invention is not restricted to the use of any particular solid material containing extractable material nor to the employment oi solid material in any particular physical form. lf desired, the solid material may be pretreated, e. g. by steam or by mechanical means to facilitate extraction. Also, the invention is not llmited to particular means for handling the solid material and causing its movement through the apparatus. for example, conveyors oi the cup type may be employed in the extractor although generally we prefer to employ the solid flight type of conveyor illustrated in Fig. 2. Various other modifications of our invention may be practiced by those skilled in the art without departing from the scope of the invention. We therefore wish it understood that our invention is not limited by the structural details and procedural steps set forth above, which are intended to be illustrative and not restrictive of our invention, but only by the scope of the appended .nected at its lower end with the lower part of a relatively short riser tube, said riser tube being 'inclined 'from the vertical plane towards said long tube at an angle of not more than about 25, means for delivering solvent into the upper part of said short tube, means for discharging lixivium from the upper part of said long tube, and conveyors for moving said solid material downwardly through said long tube and upwardly through said shortftube.

2. An apparatus for the continuous countercurrent extraction of extractable material from solids by means of a solvent whose density is greater than that of said extractable material and also greater than that of the solids being treated after said extractable material has been removed therefrom, which comprises a relatively long extractor tube inclined at an angle of about to 20 from the horizontal and directly connected at its lower end with the lower part of a relatively short riser tube, said short tube being inclined from the vertical plane towards said long tube at an angle of not more than about 25, means for delivering solvent into the upper part of said short tube, means for discharging lixivium from the upper part of saidA long tube, and conveyors for moving solid material downwardly through said long tube andupwardly through said short tube.

The arrangement of appa'- nected at its lower end with the lower part o! a relatively short riser tube, said short tube being inclined from the vertical towards s'aid long tube at an angle not greater than about 25, means for delivering solvent into the upper part of said short tube, means for discharging lixivium from the upper part ofi said long tube, said long tube being provided at its upper portion with a series of parallel slots positioned in thel under side thereof at a right angle to the axis ci said long tube, thereby forming said discharging means, and conveyors for moving solid material downwardly through said long tube and upwardly through said short tube.

fl. An apparatus for the continuous countercurrent extraction of extractable material from solids by means of a solvent whose density is 3. An apparatus for the continuous countergreater than that of said extractable material and also greater than that of the solids being treated after said extractable material has been removed therefrom, which comprises a relatively long extractor tube inclined at an angle of about 10 to 25 from the horizontal and directly connected at its lower end with the lower part of a relatively short riser tube, said short tube being inclined from the vertical towards said long tube at an angle not greater than about 25, means for delivering solvent into the upper part of said short tube, means for discharging lixivium from the upper part of said longtube, said long tube being provided at its upper portion with a series of parallel slots positioned in the under side thereof at a right angle to the axis' of said long tube, thereby forming said discharge means, and conveyors for moving solid material downwardly through said long tube and upwardly through said short tube, the upper part of said short tube being provided with a downwardly directed tube for discharging by gravity solid material from said short tube.

5. An apparatus for the continuous counter- I current extraction of extractable material from solids by means of a solvent whose density is greater than that of said extractable material and also greater than that of the solids being treated aftersaid extractable material has been removed therefrom, which comprises a relatively long extractor tube inclined at an angle of about 10 to 25 from the horizontal and directly connected at its lower end with the lower part of a relatively short riser tube, said short tube being inclined from the vertical towards said long tube at an angle not greater than about 25, means for delivering solvent into the upper part of said short tube, means for discharging lixivium from the upper part of said long tube, means for feeding solid material into the upper part of said long tube above the point at which lixivium is to be removed so as to prevent escape of solvent vapors at the point of entry of said solid material, conveyors for moving said solid material downwardly through said long tube and upwardly through said short tube, the upper part of said short tube being provided with a downwardly directed tube for discharging by gravity solid material from said short tube.

6. An apparatus for the continuous countercurrent extraction of extractable material from solids by means of a solvent whose density is greater than that `of said extractable material and also greater than that of the solids being treated after said extractable material has been removed therefrom, which comprises a relatively long extractor tube inclined from the horizontal Vat an angle of about 16 and directly connected said long tube and upwardly through said short tube.

ARTHUR A. LEVINE. ORLAND R. SWEENEY. CHARLES E. KIRCHER, J R. WILLIAM L. MCCRACKEN. 

